1. Field of the Invention
This invention relates to data storage facilities and more specifically to migrating data between data storage facilities.
2. Description of Related Art
A data storage facility generally comprises a disk array storage device that includes physical storage media and related controls. For example, a typical disk array storage device includes a plurality of physical disk drives as physical storage media. The controls include a cache memory, an interconnecting bus and adapters. At least one host adapter connects between a host processor, or “host” and the bus. A plurality of disk adapters act as interfaces between the bus and the physical disk drives.
From the perspective of applications being processed by a host, disk storage typically is organized into “logical devices”. Such “logical devices” are also known as “logical storage devices”, “logical volumes” and “devices”. The following discussion uses “logical device.” Each logical device may reside in part of, or in the entirety of, a single physical disk drive. A logical device also may reside on multiple physical disk drives. Logical devices may store one or more “data sets”, also called files. Each data set comprises one or more extents. An extent is defined by one or more contiguous storage locations, typically contiguous cylinders or tracks in a disk storage system. A plurality of data sets may be designated as a “group.”
An operating system provides control routines and data structures to interface a host application with a data storage facility. I/O requests from a host application generally define an operation, like a “read” or “write” operation, and logical device addresses for logical storage locations from which or to which the data is to be retrieved (read) or sent (written) respectively.
IBM-based systems, for example, use an MVS® operating system that includes access methods, a unit control block (UCB) and related structures that are assigned to each logical device. Operating system I/O control routines use these unit control blocks to convert the logical device addresses provided by the application into connection-based addressing recognized by the storage facility. Metadata, such as that in the volume table of contents (VTOC), provides the exact cylinder and head ranges occupied by multiple extents on that logical device assigned to a particular data set. Although a single extent occupies contiguous storage locations in a single logical device, such operating systems may scatter the individual extents in a data set across a number of logical devices.
As the quantity of stored data grows, the quantity of data in existing data storage facilities approaches a maximum capacity. Additions to that capacity often involve the addition of newer data storage facilities have greater capacities and improved performance. Consequently, it has become desirable to replace existing data storage facilities with the addition of newer data storage facilities which may be faster and have a larger capacity.
Replacing data storage facilities requires a transfer of data from the older data storage facilities to the newer data storage facility or facilities. In some cases, data migration may be performed while applications are accessing the data. See, for example, published PCT patent application PCT/US2006/024535, which is incorporated herein by reference. However, one difficulty with the system disclosed in PCT/US2006/024535 and in similar systems is that even after the data has been migrated, proper diversion to the target device requires maintaining the UCB for the source device, and thus maintaining the source device itself, until all applications that initially access the source device have terminated. The source device may not be reused until all applications have terminated (see, for example, FIG. 9 of PCT/US2006/024535).
Accordingly, it is desirable to provide a system that allows reuse of a source device prior to termination of all application that access the source device.